Drive systems of this kind have long been known. It should be noted that, instead of an internal combustion engine as a primary motor, a fuel cell can also generally serve as a primary motor. In particular, DE 10 2009 004 671 A1 describes a drive system of a plug-in hybrid motor vehicle. In this case, the control unit provides two drive modes, specifically the “depleting mode” or charge consumption mode, where electrical energy is discharged from the high-voltage source and used for driving purposes, and the “sustaining mode” or charge storage mode, in which the high-voltage battery is used only as a buffer storage means. The choice between the two modes is made essentially by the control unit. It goes without saying that once the minimum setpoint state of charge is reached and the control unit has selected the “sustaining mode”, the “depleting mode” can no longer be used. This is disadvantageous particularly when driving in a “zero-emission zone”. In this case, the high-voltage source of the motor vehicle first has to be fully recharged at a power outlet, so that the “depleting mode” is available.